Impact of Clouds on Surface Radiative
Fluxes and Snowmelt in the Arctic and
Subarctic

A comprehensive atmospheric radiative transfer model combined with the
surface energy balance equation is applied to investigate the impact of
clouds on surface radiative fluxes and snowmelt in the Arctic and
Subarctic. Results show that at the surface, the shortwave cloud radiative
forcing is negative, while the longwave forcing is positive and generally
much larger than the shortwave forcing. Thus, the all-wave surface
cloud-radiative forcing is positive, with clouds warming the lower
atmosphere and enhancing snowmelt during the melting period in the
Arctic and Subarctic. These results agree with and explain ovservations
and measurements over the past three decades showing that the onset of
snowmelt starts earlier under cloudy sky conditions than under clear sky
conditions in the Arctic. Clouds could change the date of onset of
snowmelt by as much as a month, which is of the order of the observed
interannual variations in the timing of snowmelt in the Arctic and
Subarctic. The all-wave cloud-radiative forcing during the period of
snowmelt reaches a maximum at equivalent cloud droplet radius
(re) of about 9 micrometerrs, and cloud liquid water path of
about 29 g per meter squared. For thin clouds, the impact of changes in
liquid water path on all-wave cloud radiative forcing is greater than
changes in equivalent cloud droplet size, while for thick clouds, the
equivalent cloud droplet size becomes more important. Cloud base
temperature and to a minor extent cloud base height also influence the
surface radiative fluxes and snowmelt. This study indicates that the
coupling between clouds and snowmelt could amplify the climate
perturbation in the Arctic.Journal of Climate. 9, 2110-2123, September, 1996.sbowling@gi.alaska.edu